DNA that is recognized as foreign to a given cell may be targeted for degradation within the cell, either by its lack of a host-like methylation pattern or by the presence of unusual base modifications relative to the host DNA (Bair and Black, 2007, J Mol Biol 366: 768-778). The subsequent degradation by restriction endonucleases reportedly constitutes effective barriers to the introduction of DNA into bacteria (Briggs et al. Appl. Environ. Microbiol. 1994, 60, 2006-2010; Accetto et al. FEMS Microbiol. Lett. 2005, 247, 177-183; Bair and Black, J. Mol. Biol. 2007, 366, 768-778; Corvaglia et al. Proc. Natl. Acad. Sci. U.S.A. 2010, 107, 11954-11958; Monk et al., 2012, mBio 3(2): e00277-11.doi: 10.1128/mBio.00277-11).
These nuclease-based systems are grouped into four main types, type I to type IV, by a number of criteria (Roberts et al. Nucleic Acids Res. 2003, 31, 1805-1812). Systems of type I to type III encompass paired methyltransferase and endonuclease activities, degrading foreign DNA that lacks the proper methylation pattern, whereas the type IV enzymes are endonucleases that only cleave DNA substrates that have been modified (Tock and Dryden, Curr. Opin. Microbiol. 2005, 8, 466-472).
Bacterial transformants provide a key platform for a variety of industrially relevant processes, such as metabolic engineering and biochemical production. However, the introduction of foreign DNA into some bacterial hosts, e.g., Lactobacillus, can be an inefficient process, resulting in few, if any, transformants. There is a need in the art for new methods of introducing a DNA into bacterial host cells to improve the efficiency of obtaining transformants. The present invention fulfills these and other needs.